The present invention relates to decaffeination of caffeine-containing vegetable materials, such as coffee, particularly green coffee beans.
Various means and methods for effecting extraction of caffeine from vegetable materials, particularly from green coffee beans, have been proposed. Efforts have been directed to reducing the amount of time to effect decaffeination for providing more efficient commercial manufacturing operations and reduction of costs and for enhancing the quality of the decaffeinated product.
The teachings of European Patent Publication No. 0 114 426 and U.S. Pat. No. 4,474,821 are directed to increasing the rate of decaffeination of green coffee beans by inducing a turbulent flow of an extraction medium comprising non-chlorinated esters, preferably ethyl acetate. These references postulate that caffeine removal may be modelled as a first order mass transfer process and teach that the induced turbulent flow is essential for accelerating and optimizing the decaffeination rate. These references teach that different conditions are required when utilizing single-vessel versus multi-vessel systems, particularly in regard of control of water content of the beans and that recycling of the extraction medium is required for uniformity of decaffeination in the extraction vessels. It also is disclosed that the process increases the acidity of the decaffeinated coffee as compared with coffee which is decaffeinated with the same solvent but not in accordance with the disclosed invention.
The extraction medium flow which these references indicate must be induced is characterized by a Reynolds number greater than 250 and preferably above 500. These references calculate the Reynolds number by means of the formula: EQU R.sub.E =D.sub.P G/.mu.
wherein D.sub.P is the particle diameter when a spherical diameter is assumed for the bean, G is an extraction medium mass superficial velocity based on an empty cross sectional area of an extraction column and .mu.is the extraction medium viscosity. As disclosed in these references, by reason of these relationships and this equation, for R.sub.E values less than 10 the flow is characterized as being laminar, between 10 and 100 the flow is characterized as being in a transition zone, and above 100 the flow is characterized as becoming turbulent.
Decaffeination of vegetable materials, including coffee, utilizing a fatty material is also known, as disclosed in U.S. Pat. No. 4,465,699 and British patent specification No. 1,532,547. The variables and conditions heretofore recognized as affecting and influencing efficiency of the decaffeination process with a fatty material were the weight ratio of the fatty material to the vegetable material, the temperature of contact and the overall time of contact, and the extent of regeneration of the fatty material, i.e., removal of extracted caffeine from the fatty material after extraction to permit re-use of the fatty material in the process.